Diphenylamine compounds have widely been known as medicine and agricultural chemicals and intermediates thereof, and functional pigments, electronic materials and the like and intermediates thereof (see patent documents 1, 2 and 3).
Heretofore, it has been known that reaction of 2-chloronitrobenzene compound in which ortho position to nitro group is monosubstituted with chlorine, with aniline compound proceeds due to electron attracting characteristics of the nitro group (see non-patent document 1).
In order to increase the electron attracting characteristics of nitro group by resonance effect, better planarity to benzene ring is required, and when ortho position of nitro group is monosubstituted with chlorine, although the substitution doesn't entirely have adverse effects, there is a report that the reaction proceeds under a specific condition as described in non-patent document 1.

On the other hand, in the case of reaction between 2,6-dichloronitrobenzene compound in which ortho positions of nitro group are disubstituted with chlorine and aniline compound, the nitro group and benzene ring cannot take a coplanar structure due to the presence of chlorines on both sides of nitro group, thus the nitro group cannot increase its electron attracting characteristics by resonance effect, causing a problem of decrease in electrophilic reactivity.
For the purpose of compensating for such decline in electrophilic reactivity, known are methods to increase the electrophilic reactivity of 2,6-dichloronitrobenzene compound by introducing strong electron withdrawing groups (nitro group, trifluoromethyl group or cyano group, etc.) on the position of 3 to 5 of 2,6-dichloronitrobenzene compound, and methods to increase the nucleophilic reactivity of anilines by increasing acidity of amino group of aniline compound by introducing electron withdrawing groups into anilines and facilitating the reaction of aniline compound and base (see patent document 2). However, in these methods, it is necessary to introduce electron withdrawing group into 2,6-dichloronitrobenzene compounds and aniline compounds, that is, the methods have a defect that substituents are restricted.
As a method wherein the decrease of electrophilic reactivity is supplemented and substituents are not restricted, methods that are carried out under high temperature and/or high pressure are known (see patent document 3 and non-patent document 3, 4). However, when industrially implemented, the condition of high temperature and/or high pressure has disadvantages that many risks are involved and further special production facilities cost a great deal.
As a method that is carried out under high temperature and high pressure, a method described in patent document 3 is known. However, it is known that in particular, when nitro compounds are subjected to high temperature, they have an extremely high risk.
As a method that is carried out under high temperature, a method described in non-patent document 3 is also known. However, in addition to the above-mentioned defects, the yield of this method is relatively low.
Further, as shown in the above reaction formula, the condition of high temperature and/or high pressure may cause the formation of 2,6-di(phenylamino)nitrobenzene compound (di-form) as a by-product. On the other hand, in the case of 2-chloronitrobenzene compound in which ortho position to nitro group is monosubstituted with chlorine, the reaction can be conducted under a drastic condition such as high temperature and/or high pressure since there is no need to worry about occurring 2,6-di(phenylamino)nitrobenzene compound (di-form) as a by-product because the site to which the aniline compound can react is one. However, since 2,6-dichloronitrobenzene compound in which ortho positions of nitro group are disubstituted with chlorine has two reaction site, thus there is a concern about occurring 2,6-di(phenylamino)nitrobenzene compound (di-form) as a by-product, it is not preferable to conduct the reaction under a drastic condition such as high temperature and/or high pressure.
For example, as a method for conducting the reaction under high pressure, a method described in non-patent document 4 is known, but in addition to the above-mentioned defects, this method has disadvantages that 2,6-di(phenylamino)nitrobenzene compound (di-form) is produced as a by-product in considerable quantity, on top of low yield.
As a method wherein decrease of electrophilic reactivity is supplemented, substituents are not restricted and high temperature and high pressure can be avoided, a method using palladium catalyst is known (see non-patent document 2). However, use of expensive catalyst and reagent exemplified by these noble metal catalysts is not industrially preferable because of its high cost.
Furthermore under this condition, there is a disadvantage that 2,6-di(phenylamino)nitrobenzene compound (di-form) is formed in considerable quantity as a by-product, thus this is not a good method for producing diphenylamine compound which is 2-chloro-6-phenylaminonitrobenzene compound (mono-form) intended.
As another method wherein decrease of electrophilic reactivity is supplemented, substituents are not restricted and high temperature and high pressure can be avoided, a production method that makes the reaction easier by raising the acidity of amino group of aniline compounds by converting to formamide is known with respect to the example reaction of 2-chloronitrobenzene compound in which ortho position of nitro group is monosubstituted with chlorine and aniline compound (see non-patent document 5).
However, this method is not so convenient because the number of steps is increased, further there are disadvantages that it has a step which needs high temperature in addition to that the yield is relatively low.
As analogous methods to the above, a production method is known wherein an aniline compound is formamidated, and reacted with 2,6-dichloronitrobenzene compound, then deformylation is carried out (see patent document 1). However, it is confirmed that the yield is not so high in this method (see Comparison Example 9).
As furthermore method wherein decrease of electrophilic reactivity is supplemented, substituents are not restricted and high temperature and high pressure can be avoided, and as a reaction example using aminopyrazole compound instead of aniline compound in the reaction of 2-chloronitrobenzene compound and aniline compound, the condition is known that sodium hydride is used as base, tetrahydrofuran is used as solvent, and reaction is conducted at room temperature (see non-patent document 6). However, in the reaction of 2,6-dichloronitrobenzene compound and aniline compound, the intended compound couldn't be obtained under the condition described in non-patent document 6 (see Comparison Example 2).